The Piezoelectric Accelerometer is used to detect unevenness in the road surface which is transferred to the engine via the sub-frame. Whenunevenness exceeds a certain level the misfire diagnostic is switched OFF.

The accelerometer receives 5 V from the Engine Control Module (ECM). Its output signal is approx. 2.5 V for a stationary car. When there is verticalmovement the signal will oscillate around 2.5 V.